```
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      * {
        box-sizing: border-box;
      }

      body {
        padding: 20px;
      }

      #bk {
        margin-left: 1000px;
        height: 100px;
        width: 100px;
        display: inline-block;
        background: url(https://tse3-mm.cn.bing.net/th/id/OIP.bPN_MjALkh1SftGFqv7n9wHaEK?w=293&h=180&c=7&o=5&pid=1.7);
        background-position: center;
        background-size: cover;
        perspective: 200px;
        -webkit-perspective: 200px;
      }
      #boxa {
        height: 100%;
        width: 100%;
        background: url(https://tse2-mm.cn.bing.net/th/id/OIP.RoIXw4GXBuuKtbjvwBe_VQHaEr?w=261&h=180&c=7&o=5&pid=1.7);
        background-position: center;
        background-size: cover;
        background-repeat: no-repeat;
        background-color: white;
      }

      .animation-style {
        /* transform: translate3d(0,0px,100px); */

        -webkit-transform: rotateY(-180deg);
        transform: rotateY(-180deg);

        transform-origin: 0 100%;
        -webkit-transform-origin: 0 100%;

        transition: transform 2s;

        transition-delay: 500ms;
        transition-duration: 1s;
        /* transition-timing-function: ease-in-out; */
      }

      .animation-end {
        opacity: 0.6;
      }
    </style>
  </head>
  <body onload="loadedPage()">
    <!-- <div id="boxa" class="animation-style"></div> -->
    <div id="bk">
      <div id="boxa"></div>
    </div>
  </body>
  <script>
    function loadedPage() {
      setTimeout(() => {
        console.log("!23");
        var mydiv = document.getElementById("boxa");
        mydiv.className = "animation-style";
      }, 1000);
    }
  </script>
</html>

```